1. Field of the Invention
This invention relates to a totally implantable hearing system for rehabilitation of hearing disorders, comprising at least one sensor for picking up at least airborne sound and converting it into electrical signals, an electronic module including electronic means for audio signal processing and amplification, an output-side actuator arrangement for stimulation of the middle or inner ear, and an electrical power supply unit.
2. Description of Related Art
The expression xe2x80x9chearing disorderxe2x80x9d is defined here as including all types of inner ear damages up to complete postlingual loss of hearing or prelingual deafness, combined inner ear and middle ear damages, and temporary or permanent noise impressions (tinnitus).
In recent years, rehabilitation of sensorineural hearing disorders with partially implantable electronic systems has acquired major importance. In particular, this applies to the group of patients in which hearing has completely failed due to accident, illness or other effects or in which hearing is congenitally non-functional. If, in these cases, only the inner ear (cochlea), and not the neural auditory path which leads to the brain, is affected, the remaining auditory nerve can be stimulated with electrical stimulation signals. Thus, a hearing impression can be produced which can lead to speech comprehension. In these so-called cochlear implants (CI), an array of stimulation electrodes is inserted into the cochlea. This array is controlled by an electronic system which is surgically embedded as a hermetically sealed, biocompatibly encapsulated electronic module in the bony area behind the ear (mastoid). The electronic system contains essentially only decoder and driver circuits for the stimulation electrodes. Acoustic sound reception, conversion of this acoustic signal into electrical signals and further processing of the latter, always takes place externally in a so-called speech processor which is worn outside on the body. The speech processor superimposes the preprocessed signals, properly coded, on a high frequency carrier signal which, via inductive coupling, is transmitted (transcutaneously) to the implant through the closed skin. The sound-receiving microphone is always located outside of the body and, in most applications, in a housing of a behind-the-ear hearing aid worn on the external ear. The microphone is connected to the speech processor by a cable.
In addition to rehabilitation of congenitally deaf persons and those who have lost their hearing using cochlear implants, for some time there have been approaches to offer better rehabilitation than with conventional hearing aids by using partially or totally implantable hearing aids for patients with a sensorineural hearing disorder which cannot be surgically corrected. The principle consists, in most embodiments, in stimulating an ossicle of the middle ear or, directly, the inner ear via mechanical or hydromechanical stimulation and not via the amplified acoustic signal of a conventional hearing aid in which the amplified acoustic signal is supplied to the external auditory canal. The actuator stimulus of these electromechanical systems is accomplished with different physical transducer principles such as, for example, by electromagnetic and piezoelectric systems. The advantage of these devices is seen mainly in a sound quality which is improved compared to that of conventional hearing aids, and, for totally implanted systems, in the fact that the hearing prosthesis is not visible. Such partially and totally implantable electromechanical hearing aids are described, for example, by H. P. Zenner et al. xe2x80x9cFirst implantations of a totally implantable electronic hearing system for sensorineural hearing lossxe2x80x9d, in HNO Vol. 46, 1998, pp. 844-852; H. Leysieffer et al. xe2x80x9cA totally implantable hearing device for the treatment of sensorineural hearing loss: TICA LZ 3001xe2x80x9d, in HNO Vol. 46, 1998, pp. 853-863; and H. P. Zenner et al. xe2x80x9cTotally implantable hearing device for sensorineural hearing lossxe2x80x9d, in The Lancet Vol. 352, No. 9142, page 1751.
Many patients with inner ear damage also suffer from temporary or permanent noise impressions (tinnitus) which cannot be surgically corrected and for which, to date, there are no approved drug treatments. Therefore, so-called tinnitus maskers have become known. These are small, battery-driven devices which are worn like a hearing aid behind or in the ear and which, by means of artificial sounds which are emitted, for example, via a hearing aid speaker into the auditory canal, psychoacoustically mask the tinnitus and thus reduce the disturbing noise impression, if possible, to below the threshold of perception. The artificial sounds are often narrow-band noise (for example, third-band noise). The spectral position and the loudness level of the noise can be adjusted via a programming device to enable adaptation to the individual tinnitus situation as optimally as possible. In addition, the so-called retraining method has been developed recently in which, by combination of a mental training program and presentation of broad-band sound (noise) near the auditory threshold, the perceptibility of the tinnitus in quiet conditions is likewise supposed to be largely suppressed. These devices are also called xe2x80x9cnoisersxe2x80x9d.
In the two aforementioned methods for hardware treatment of tinnitus, hearing aid-like, technical devices must be carried visibly outside on the body in the area of the ear. They stigmatize the wearer and, therefore, are not willingly worn.
Recently, partially and totally implantable hearing systems for rehabilitation of inner ear damage have been introduced in clinical use. In the case of the totally implantable hearing system TICA(copyright) (H. P. Zenner et al. (xe2x80x9cTotally implantable hearing device for sensorineural hearing lossxe2x80x9d, The Lancet, Vol. 352, November 1998, No. 9142, page 1751) an audio sound sensor (microphone) is used which is subcutaneously inserted in the rear bony wall of the auditory canal as disclosed in more detail in U.S. Pat. Nos. 5,814,095 and 5,999,632. First clinical experiences with this system show that the own voice as well as other body sound vibrations, such as chewing and swallowing noise, are clearly and disturbingly loudly perceived by some patients. This is due to the fact that not only airborne signals incident from the exterior are picked up by the audio sensor, but also body sound-induced signals are acting on the audio sensor by bone transmission and, upon amplification by the implanted hearing system, likewise are transmitted to the inner ear. In view of this mixture of the individual input signal components the familiar and desirably natural sound pattern of the own voice changes in the case of these patients, or the amplified body sound portion is acting as interference which may be masking, whereby the hearing and understanding of external language is impeded. This effect cannot be countered in prior hearing implants because the implanted audio sensor and the input-side functioning thereof cannot be influenced. This disturbing effect likewise is to be expected in future totally implantable cochlea implants since it can impede the hearing rehabilitation required for such implants in a still more pronounced manner than in the case of electromechanical implants for patients with defective hearing. Perhaps, a way out would be an implantation of the audio sensor in a manner in which this sensor is completely decoupled from body sound, by using proper body sound-insulating implant materials and/or structural features in the audio sensor itself. At least theoretically the described negative effect would be eliminated thereby. However, all body sound-induced components of the own voice, such as particularly mechanical laryngeal oscillations which are indispensable for a familiar, natural sound pattern of the own voice, likewise are suppressed thereby.
In order to increase the acceptance of totally implantable hearing systems using actoric output stimuli of any type, a technical solution of the above problems is desirable. Accordingly, a primary object of the present invention is to devise a hearing system which individually on the one hand prevents an unwanted amplification of body sound-induced signals and which on the other hand permits the transmission of such a part of these signals that a comfortable and natural hearing impression, particularly of the own voice, is attained.
In conformity with the subject invention a totally implantable hearing system for rehabilitation of hearing disorders, comprises:
at least one implantable sensor for picking up at least airborne sound and for converting it into electrical airborne sound signals;
at least one implantable sensor for picking up at least body sound-induced signals and for converting them into electrical body sound signals;
an electronic module including electronic means for processing and amplification of said airborne sound signals and said body sound signals, said electronic means including means for individually adjusting the ratio of airborne sound signals to body sound signals;
an output-side actuator arrangement for stimulation of the middle or inner ear; and
an electrical power supply unit which supplies individual components of the system with energy.
Particularly, the ratio of airborne sound signals to body sound signals may be adjusted such that, upon further signal processing and passing of the signals to the output-side actuator arrangement, a hearing impression, especially of the own voice, can be generated which is well-balanced between external airborne sound signals and endogenuos sound signals.
The body sound sensor or sensors is (are) preferably localized in the bony part of the skull. The sensor, for example, may be arranged separate from the electronic module and may be fixedly or detachably connected therewith e.g. by a separable plug-type connector. An advantageous implantation site is the bony part of the mastoid behind the outer ear. In this embodiment, the sensor is disposed within a hermetically sealed housing having a biocompatible surface, and the housing preferably is directly fixedly attached, e.g. by screws, to the bone at the application site in order to provide for a particularly good transmission of body sound.
The body sound sensor, however, also may be disposed in the same housing as the sensor for airborne sound provided that it is in mechanical contact with bony parts of the skull, such as for example the microphone known from commonly owned U.S. Pat. Nos. 5,814,095 and 5,999,632 which hereby are incorporated by reference. Another advantageous application site for the body sound sensor or sensors is within the housing of the electronic module of the implant. In the case of implantable hearing systems this housing basically is imbedded in the bone of the mastoid, so that a proper transmission of body sound is to be expected. A further advantage of the two last-mentioned embodiments is that in such a case the body sound sensor itself needs not to be hermetically sealed and biocompatible as this is required in the first mentioned embodiment in which the body sound sensor is separately applied in an own housing.
The at least one body sound sensor may utilize any known electromechanical transducer principle; preferably it is an electromagnetic, electrodynamic, piezoelectric, magnetostrictive or dielectric (capacitive) sensor. In a manner known per se from U.S. Pat. Nos. 4,816,125 and 4,998,179 the body sound sensor may be an on-chip semiconductor transducer. Preferably, the body sound sensor is operating in conformity with the known principle of an acceleration pick-up, wherein a mechanical-electrical transducer is coupled within the sensor housing to an inert (seismic) mass suspended for oscillating. Preferably, a piezoelectric element is used as mechanical-electrical transducer. A body sound sensor in the form of an on-chip semiconductor transducer advantageously may be integrated into a semiconductor component of the electronic module or of an airborne sound sensor module. Furthermore, commercial, body sound-sensitive, capacitive electret microphones of the conventional hearing device industry may be used. The latter embodiments are advantageous in that they may be miniaturized what favors the insertion of the hearing implant in the head region.
The spectral transmission range of the body sound sensors is in the audio range, preferably from about 100 Hz to about 10 kHz. Advantageously, the sensors are tuned to have a first mechanical resonant frequency at the upper end of the desired transmission frequency range. Thereby the transducer frequency characteristic of the sensors is essentially free from resonances and thus shows very low ripple.
The ratio of airborne sound signals to body sound signals may be adjusted in any desired manner, for example by using telemetry means which permit the transmission of data between an external unit and the implant, or, in the case of a highly intelligent implant system, by the implant reacting on corresponding speech signals of the implant wearer.
The further electronic processing of the airborne sound signals and the body sound signals may be effected via analog preamplifiers and analog orxe2x80x94after a corresponding analog-to-digital conversionxe2x80x94digital signal processing, wherein processing of the sensor signals is effected in the signal processing unit in a manner taking into consideration both amplitude and phase signals, so that possibly required corrections of various phase and group delays can be made. After spectral filtering, such a signal processing also can be carried out in a plurality of frequency bands. The respective signal processing parameters can be electronically stored within the implant and preferably can be adapted from the outside via a interface of the implant to thus arrive for the individual patientxe2x80x94after implantation, a telemetry healing period and first hearing experiencesxe2x80x94at an optimum rehabilitation result by iterative programming of these parameters.
Preferably, processing of the sensor signals is effected in a purely digital manner in a digital signal processor the software operating system of which or parts of this software operating system being adapted to be telemetrically charged or changed as described in more detail in commonly owned U.S. Pat. No. 6,198,971 which hereby is incorporated by reference. Thereby, with progress in scientific knowledge or field experiences, always an optimum signal processing algorithm may be offered to the patient without the need to exchange the implant.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.